overlays can be done, animtools has a black fade option for swapping positions.
the real question is, will all the mouse clicking work with one always on, and can any fancy filtering be done instead of just using alpha.
should be able to be done just using actionscript and using rectangles, but i'll pass on this one as it isn't interesting to me.
sidenote, if someone wants to look into it, there will be a decision to where to place the filter. important notes might be below the dialog box, as well as below the menus.
more sidenotes, might be more interesting to import a png, that way can do things like angled spot lighting or people can throw together their own shading orientation.